The manufacture of cheese from milk through preparation of a retentate by membrane processes, such as ultrafiltration and diafiltration, by removal of salts, lactose, and water has been taught in various patents and literature references. From the large variety of methods and procedures which have been proposed for the manufacture of cheese from retentates, it is apparent that the physical chemistry of milk is complex and the interactions between the protein, fat, salts and other components of milk are vastly altered by creation of the retentate. It is also apparent that methods and procedures which have been proposed for treatment of a retentate prepared from one form of milk are not predictably usable when other forms of milk, and other procedures are used to prepare a retentate. For example, some procedures, such as disclosed in U.S. Pat. No. 4,820,530 and U.S. patent application Ser. No. 649,838, filed on Sept. 11, 1984, both to Moran, et al. disclose the desirability of preventing coagulation from occurring when the retentate is fermented.
PCT application Ser. No. W082/01806 of Schrieber Foods, Inc. discloses a process which permits evaporation of water from fermented retentate. The process includes four steps: (1) selective concentration of milk to form a retentate; (2) increasing the ionic strength of the retentate by the addition of a salt, such as sodium chloride, so as to maintain it in the liquid phase during fermentation; (3) fermenting the retentates and (4) removing water from the fermented retentate to produce cheese or cheese base containing substantially all the casein and whey proteins originally present in the milk. The PCT application also discloses the use of rennet, which may be added to the retentate substantially prior to evaporation, such as at the same time as the lactic acid producing bacteria.
A patent to Coulter, et al., entitled "Cheese Manufacture from Molecular Sieved Milk," issued Oct. 26, 1976, U.S. Pat. No. 3,988,481, teaches the preparation of cheese from milk which has been de-lactosed and de-watered by a process involving molecular sieving a standardized milk to substantially separate and remove lactose and water-soluble minerals from the milk to render the milk substantially sugar-free, and adding a curd-forming agent to produce curd. The resulting curd is subjected to conventional handling without substantial syneresis to produce a cheese and is molded to a desired form.
A patent to Stenne, entitled "Method for the Manufacture of Cheeses," issued Aug. 12, 1975, U.S. Pat. No. 3,899,596, discloses a process for the production of cheese which comprises treating milk by ultrafiltration to obtain a product having at least some of the protein constituents of the milk, renneting the liquid product after inoculation with suitable ferments, and introducing a batch of the renneted liquid into a vertical chamber in which it is left to coagulate. The coagulum is cut into slabs which provide the end product cheese.
A patent to Maubois, et al., entitled "Manufacture of Cheese from Ultrafiltered Milk," issued Oct. 21, 1975, U.S. Pat. No. 3,914,435, teaches cheese made from heat-treated milk and without conventional draining of whey by a process which involves ultrafiltering of the milk to produce a concentrate having essentially the composition of cheese produced by conventional whey draining processes. The process enables the milk, after ultrafiltration, to be heat-treated without making the milk more difficult to coagulate with rennet, which difficulty normally occurs when milk is heated to high temperatures.
A patent issued to Wargel, et al., entitled "Process and Products from the Manufacture of Cheese-flavored Products," issued June 13, 1981, U.S. Pat. No. 4,244,971, teaches the manufacture of cheeses and process cheese, from ultrafiltered milk.
A patent entitled "Process for Preparing Cheese base," issued Aug. 30, 1983, to Rubin, et al., U.S. Pat. No. 4,401,679, discloses a process for preparing cheese base by concentrating milk through ultrafiltration combines with diafiltration and evaporation, wherein the retentate from the ultrafiltration is inoculated with an acid culture before evaporation, and after evaporation acidification proceeds to completion after packing.
Further, cheese base material has been taught by evaporating moisture from retentate under turbulent conditions to provide a lower moisture condition. Such a process is described in an article by Ernstrom, et al., entitled "Cheese base for Processing: A High-yield Product from Whole Milk by Ultrafiltration," published in the Journal of Dairy Science, volume 63, 223-234 (1980). The article teaches a process wherein whole milk of normal pH, or acidified to a pH of 5.7, is concentrated by ultrafiltration to about 40 percent of the original milk weight and diafiltered at constant volume until a desired ratio of lactose to buffer capacity is established. The retentate is then further concentrated by ultrafiltration to 20 percent of the original milk
weight. The retentate is then inoculated with cheese starter and incubated to completely ferment the residual lactose, pH control being achieved by controlling the level of lactose from the diafiltration step of the process. The product is further concentrated in a swept-surface vacuum-pan evaporator or a Luwa evaporator. It is pointed out in the article that the use of a batch evaporator is necessitated when the retentate, upon fermentation, curdles or coagulates, since such a product cannot be readily processed in any continuous-flow evaporator.
It is known to add salt during fermentation to prevent coagulation and this was understood many years ago. See: LeLait/November-December, 1974No. 539/540. Further, it has been disclosed that salt in the retentate may facilitate evaporation as disclosed in an Australian application, which is the subject of a published application under the Patent Cooperation Treaty W032/01306, published June 10, 1982.
The prior art specifically teaches that addition of rennet or other coagulating enzymes to high-solids milk systems causes rapid coagulation and is a condition to be avoided during evaporation, since the evaporation is said to be highly inefficient after coagulation occurs. On the other hand, the presence of coagulating enzymes may be desired, particularly in higher-solids cheese, to provide the conventional presence of para kappa casein by cleavage of kappa casein. The kinetics of enzymatic coagulation of milk is disclosed by Alfred Carlson, in a thesis published in 1982, at the University of Wisconsin, entitled "The Kinetics of Enzymatic Coagulation of Milk."
In the conventional making of cheese with rennet, the macro peptides formed by rennet action are lost in the whey with consequent reduction in yield and loss of nutritious milk protein material. Accordingly,
it would be desirable to enjoy the benefit of rennet action while avoiding whey removal with consequent loss of macro peptides.
Further, prior art methods for making cheese base materials at higher-solids with evaporation, in which evaporation is effected with high turbulence or the cheese base material is recovered with substantial working after evaporation, has resulted in destabilization of the higher-solids cheese base material, and a body and texture unlike various known cheeses. This destabilization is particularly noticeable at total solids in excess of about 60% to 62%, e.g., a cheese such as Cheddar cheese, but is also present at solids as low as 55 percent. Accordingly, cheese base materials heretofor produced by evaporating retentates to a total solids in excess of 60 percent have not provided the typical body and texture characteristics of known high-solids cheeses.
In addition, the use of high turbulence throughout evaporation or working after evaporation does not provide a product having a likeness to curd. Prior art methods for making cheese from retentates with evaporation techniques do not disclose a method for making a curd-like product.
The prior art teaches many different steps in respect to the manufacture of cheeses and cheese base materials from milk retentates. Evaporation of milk retentates is a previously known technique, but the resultant product does not have curd character, nor does it convert to a product having the body and texture of cheese. Also, much of the prior art is directed toward the manufacture of higher moisture or soft cheeses, and it has not been directed toward the production of high-solids cheeses from retentates by means of evaporation of retentates. The difficulty which occurs with turbulence at higher-solids, i.e., above 55 percent total solids, is that the product destabilizes and exudes fat, and high-solids product, i.e., above 60 percent total solids, does not have the characteristic cheese body and texture. If the moisture is high enough, fat exudation can be avoided and the body and texture of soft cheeses can be provided.
The use of skim milk, i.e., a milk having less than 1.0 percent fat, after being processed to a retentate has not been effectively evaporated in swept surface evaporators to a solids content in excess of 45 percent by known technology because of binding of the rotors in such evaporators. Thus, the known technology did not provide effective means for making skim milk cheeses, i.e., cheeses having less than 16 percent fat. Such low-fat cheeses are particularly desired for the manufacture of processed cheeses because of a consumer desire for healthful diet alternatives and their manufacture by ultra filtration and evaporation methods would provide great advantages.
Accordingly, despite the many teachings of the prior art relating to the manufacture of cheese base material and cheese from retentates derived from milk with evaporation thereof there has been a lack of an efficient process for producing cheese from skim milk utilizing a retentate produced by membrane techniques.
It is a principal object of this invention to provide a curd and/or cheese from a low-fat or skim milk retentate by means of evaporation, the curd and/or cheese having a solids content of more than 50 percent.
A further object of this invention is to provide cheese from low fat milk which is stable and does not oil-off, and is manufactured by processing a low-fat milk retentate with evaporation in a swept surface evaporator.
Another object of this invention is to provide a cheese from low-fat milk which has substantial formation of para kappa casein but which may be utilized in a process using continuous, swept surface evaporation and equipment.
Still further objects and advantages of the invention will become apparent by reference to the following description.